The mechanism of the development of chloasma and such on skin, although there are some unknown details, is generally believed to be the formation of melanin pigment due to hormonal abnormalities or ultraviolet light stimulation from sunlight followed by abnormal deposition of this pigment in the skin. This melanin pigment which causes the coloring of the skin is produced in melanin producing granules (melanosomes) in melanin cells (melanocytes) between the epidermis and the corium. Melanin thus produced is then diffused to neighboring cells by means of osmosis. The biochemical reactions in the melanocytes are speculated as described below.
That is, the production process of the melanin pigment is as follows: tyrosine, one of the essential amino acids, becomes dopaquinone through the action of an enzyme tyrosinase, and this is then changed to a red pigment, to a colorless pigment and finally to melanin, which is black, by enzymatic as well as non-enzymatic oxidation.
Therefore, in order to suppress the production of melanin, it is important to suppress the first stage of the reactions, i.e. the action of tyrosinase.
However, compounds which suppress tyrosinase action, except for hydroquinone, work very slowly and do not give sufficient improvement in pigment deposition in the skin. On the other hand, hydroquinone, although its effects are recognized, has the problem of sensitization and, therefore, its uses are generally limited. For the purpose of improving its safety, attempts have been made to alter it to a monoester of a higher fatty acid, an alkyl monoether and such (Japanese unexamined patent publication Tokkai Sho 58-154507). However, esters are decomposed by hydrolytic enzymes in the body and therefore are not necessarily safe. Sufficiently safe ethers have not been obtained yet either.
For the purpose of solving these problems, the inventors investigated a wide variety of substances for the melanin production suppression effect, and discovered that Pinon Negro (scientific name: Jastropha curcas L.) extract, Pinon Blanco extract, Cola de caballo extract (scientific name: Equisetum giganteum) extract, and Piri-Piri (scientific name: Cyperas spacelatus Rottb (C. articulatus L.)) extract, had the melanin production suppression and tyrosinase inhibition actions. There has been no report on the melanin production suppression actions of these substances or their application as whitening agents.